SUMMARY: Fourteen strains of serotype were examined for their cell-surface protein antigens in terms of hydrophobicity, and immunochemical specificities. Thirteen strains were hydrophobic, while strain GS-5 was markedly hydrophilic as compared to the other strains tested. Cell-surface protein antigens were then analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis () and Western immunoblotting. A protein antigen of 190000 (PAc) was found in cell extracts and culture supernatants of all the hydrophobic strains. Neither culture supernatant nor cell extract of strain GS-5 contained PAc. Strain GS-5, however, produced extracellularly a large amount of a protein of 155000 (PAGS-5) which reacted with rabbit anti-PAc serum. Immunodiffusion analysis showed that -5 lacked a part of the antigenic moieties in the c molecule. and radioimmunoassay showed a small amount of -5 on the cell surface of strain -5. These findings suggest that -5 may correspond to c which lacks a region participating in binding of c to the streptococcal cell.


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